Loose mapping for unmappable content

When source content doesn't map cleanly to any Mimir entity, use loose mapping: find the nearest ontology type and capture the nuance in the description field. Nothing should be dropped — it just lands at the right level of fidelity.

Loose mapping guide:
- Background / Related Work → summarize in playbook or phase description
- Problem / task definitions → map as a Rule with the formal definition in the content field
- Mathematical or formal content → summarize in activity guidance or rule content; transcribe verbatim only if the exact formulation is operationally critical
- Motivating examples → skip, or include as an illustrative note in activity guidance
- Conclusions / discussion → extract any constraints or rules; discard the rest